This invention relates to front bicycle derailleurs of the type comprising:
a supporting body fastened to the bicycle frame,
a fork unit for derailing the bicycle chain,
means for connecting the fork unit to the supporting body, including at least one arm, which ends pivot on the supporting body and the fork unit,
an actuating arm, consisting of an extension of said pivoting arm and,
and electrical motor associated to the supporting body for controlling said actuating arm.
A front derailleur of the type described above is illustrated in FIG. 5 of U.S. Pat. No. 5,470,277 by the Applicant, and in FIG. 11 of Italian Patent Application no. TO99A001023, also by the Applicant, still secret at the registration date of this application. FIG. 1 of the accompanying drawings, provided for quick reference, shows a front derailleur of the type presented in the Italian Patent Application mentioned above. In this figure, the front derailleur is generally indicated with reference numeral 1. It comprises a supporting body 2 with a band 3 for fastening to a tube of a bicycle frame. Numeral 5 generally refers to a fork unit, of the known type, for chain derailing (not illustrated) of the bicycle for the selective engagement of said chain with the sprockets (not shown) associated to the central movement of the bicycle. The fork unit 5 is connected to the supporting body 2 by means of an articulated parallelogram system, comprising two arms 6, 7 respectively pivoting in 8, 9 and 10, 11 to the supporting body 2 and to the fork unit 5. The articulated arm 7 arranged on the external side extends to actuating arm 12, forming a single part with arm 7 at an angle of approximately 90xc2x0. A worm screw element 13, fastened onto a screw 14, connected to the output shaft of an electrical motor 15 of the front derailleur, pivots on the arm 12. The electrical motor 15 is equipped with a band 16 for connecting the motor body in a pivoting fashion on an axis 17 of the derailleur 2, because the motor must be able to oscillate on the axis 17 when, following operation, the arm 12 makes an angular oscillation on the articulation on the support unit 2.
Said solution, previously presented by the Applicant, was not fully satisfying on operative level, for various reasons. Firstly, the electrical motor must make a high number of turns to move the fork unit between its two extreme positions. Secondly, as mentioned, due to the system geometry, the motor 15 must be fitted to pivot on axis 17, and operatively occupies a relatively large space, with the additional problem of possible coupling play. Finally, with the geometry illustrated in FIG. 1, a wide maximum excursion of the front derailleur cannot be obtained if the dimensions are to be kept relatively low, without seizing. This is required, for example, in the cases in which three sprockets are associated to the central movement.
In order to solve all said problems, this invention relates to a front derailleur, which characteristics are indicated at the beginning of this description, also characterised in that said electrical motor controls said actuating arm by means of a geared transmission, comprising a first gear connected to the electrical motor shaft and a second gear connected to said actuating arm.
Thanks to this characteristic, the transmission between the electrical motor and the controlled unit performs better than the case illustrated in FIG. 1. Furthermore, by appropriately selecting the transmission ratio achieved by means of said gears, a considerable reduction of revolutions of the motor to take the derailleur from one end of the stroke to the other can be obtained. At the same time, the electrical motor can be fitted so to be fixed with respect to the bicycle frame, i.e. so that it does not oscillate as shown in FIG. 1, with consequent reduction of dimensions and play due to coupling. Finally, the geared transmission, along with the reduced dimensions mentioned above, provide a longer derailleur stroke, also suitable for triple sprocket transmission, without seizing.
In a first form of embodiment, said first gear solidly fastened to the electrical motor shaft is a worm screw and the second gear is a sector gear, preferably forming a single part with said articulated arm and said actuating arm. In a variant of said form of embodiment, the worm screw connected to the electrical motor shaft engages an auxiliary sector gear connected so to turn with a pinion, which in turn engages the sector gear on the actuating arm. This variant is obviously preferred in the case of a two-stage cascade transmission.
In the case of a second form of embodiment, the first gear consists of a tapered pinion connected to the electrical motor, while the second gear is a tapered gear connected to the actuating arm. A variant can be envisaged, in which the tapered pinion connected to the motor shaft engages an auxiliary tapered pinion which is connected so to turn with a tapered gear engaging a sector gear connected to the actuator arm. Also in this case, a double-stage reduction is obtained.
Finally, a geared transmission for selectively operating two different transmission ratios can be envisaged. The preferred transmission ratio selection is obtained by sliding a unit, connected to two coaxial pinions, so to operatively engage one of said pinions on a sector gear, connected to the actuating arm, accordingly. Said selection can be made manually by cyclists according to their specific needs.